1. Field of the Invention
The present disclosure relates to rare earth metal complexes of 5,6-diaryl-3-(2-pyridyl)-1,2,4-triazines and a process for preparing the same. The present disclosure also relates to europium dipyridyl nitrates with diketone dopants and a process for preparing the same. The rare earth metal complexes of this disclosure may be used as pigments in ink compositions for printing systems and for security applications.
2. Description of the Related Art
Certain rare earth metal complexes that are invisible under normal lighting conditions, yet produce strong emissions in the visible region when irradiated with ultraviolet (UV) light, are known and have been used in ink compositions. For example, JP 8239607A describes europium diketonate complexes with butylammonium salt as the counter anion that have been used in ink jet applications. U.S. Patent Application Publication No. 2003/0089273 describes europium-ammonium chelates that are not visible under ordinary light conditions, yet fluoresce when exposed to certain wavelengths of UV light, and which have increased solubility in alcohol and alcohol/water solutions as compared with known europium complexes. Known europium complexes include Eu(AA)3Phen, Na(Eu(AA)4), HPip(Eu(AA)4), Eu(BA)3Phen and Na(Eu(BA)4), where Eu is Europium, AA is acetylacetone, HPip is homopiperazine, and Phen is 1,10-phenanthroline. U.S. Pat. No. 5,837,042, which is incorporated herein by reference, describes ink jet compositions, used in security markings, having a colorant of a rare earth metal and certain chelating ligands that emit light when irradiated by UV light. U.S. Pat. No. 6,905,538 describes inks containing certain rare earth complexes, used in postal applications, which are invisible to the unaided eye, yet fluoresce when irradiated with short wavelength UV radiation.
Presently, rare earth metal complexes that fluoresce brightly when irradiated with UV light are coordinated with organic ligands such as diketones, carbonic acid, and pyridyl or phenanthryl coordinators. A known rare earth metal diketonate complex of this type is europium tris-benzoyltrifluoro-acetone-diketonate. See R. G. Charles, J. Inorg. Chem. (1966), vol. 28, pages 3005-3018.
Disadvantages of the known rare earth metal complexes include: (1) poor solubility in water; (2) insufficient stability in water for inkjet applications; and (3) an excitation range that is limited to the UV-C or short UV wavelength range (wavelengths less than 220 to 300 nanometers). As such, there is a need for rare earth metal complexes that: (1) possess a high degree of solubility in water and/or organic solvents; (2) are sufficiently stable in water to enable their use in inkjet applications among others; and (3) exhibit excitation in the long UV wavelength range (between 350 to 390 nm).